The present invention relates generally to methods and devices for improving indoor air quality. More particularly, the present invention relates to methods and devices for controlling humidity and/or for removing volatile organic compounds and particulate material from the inside space.
Indoor air quality is a subject of increasing concern. Indoor air quality is impacted by several air contaminants such as humidity, volatile organic compounds (VOCs), semi volatile organic compounds (SVOCs), and particulate material. While it is desirable to control the level of humidity at a precise level, it is also desirable to cause a high rate of removal of the other components such as VOCs and particulate materials.
Normally, indoor air quality in commercial buildings is managed by controlling the fresh air ventilation rate. Leakage and sometimes outside combustion air supply provides sufficient refresh air supply for most residential structures. However, it will be more important to control the air composition as homes and buildings become tighter and as concern over the presence of organic impurities and particulates becomes greater. Currently, carbon adsorption, sometimes known as carbon filtration, is used to remove organic vapors from air streams. The strategy is usually to add enough carbon granules to an adsorption bed to remove organic compound impurities from the air for a period of weeks or months. Under normal circumstances, the carbon is used for three to six months and then replaced. Unfortunately, the performance and usage of this type of system is limited by cost of purchase and disposal of large carbon canisters and by the amount of back-pressure that can be tolerated in the forced air system.
Although it is important to remove organic impurities from building air, it is also important to remove or add the proper amount of water vapor. Humidity control is necessary because air that is too wet causes mold and other undesirable contaminants. This generates biologically-derived organic compounds and air dispersed biological molecules, which can cause health and building structure problems. Air that is too dry causes a decrease in the function of mucous membranes, which decreases human disease resistance.
While organic compounds typically should be removed at a level as high as possible, humidity should be controlled within a range, such as between 40-60% relative humidity. In the winter, humidity can be increased to this range by use of wicking or ultrasonic dispersion methods in commercial and residential buildings. In the summer, humidity can be decreased to this range by over-cooling the air at the cooling coil in the main air handling unit, and then re-heating the over-cooled air to a more reasonable supply level. The air is over-cooled to wring out the desired excess water. Reheat is often accomplished with a heating coil located in the main air handler and immediately downstream of the cooling coil (central reheat), or with smaller re-heat coils located in the discharge/supply registers (called terminals) located within the occupied space. A limitation of this approach is that over-cooling the air and then re-heating the over-cooled air can consume significant energy. Further, the cost and complexity of such systems can be high. For these and other reasons, the humidity in residential buildings is typically not controlled during the cooling season.
The present invention provides methods and devices for improving indoor air quality by providing a robust, relatively simple system that can control the air quality in buildings during both the heating and cooling seasons. In doing so, the present invention can control the humidity and remove volatile organic compounds and particulate material from the inside space.
In one illustrative embodiment of the present invention, and during a first cycle, a first air stream is directed through an air treatment module and back into the inside space. During this first cycle, a desiccant in the air treatment module adsorbs water, volatile organic compounds and/or particulate material from the first air stream. During a second cycle, a second air stream is directed through the air treatment module to a location outside of the inside space. The second air stream is preferably heated relative to the first air stream so that at least a portion of the adsorbed water, volatile organic compounds and/or particulate material are desorbed from the desiccant into the second air stream. The second air stream carries the desorbed water, volatile organic compounds and/or particulate material to a location outside the inside space.
The air treatment module preferably includes a chamber with an inlet, a first outlet and a second outlet. A first valve selectively obstructs the first outlet, and a second valve selectively obstructs the second outlet. The first air stream is directed through the air treatment module and back into the inside space by closing the first valve and opening the second valve. During this cycle, the air treatment module adsorbs water, volatile organic compounds and/or particulate material from the first air stream.
The second air stream is then directed through the air treatment module to a location outside of the inside space by opening the first valve and closing the second valve. The second air stream can be heated to a temperature above the first air stream in any number of ways, including for example, activating a heating element during a cooling cycle, or restricting the flow of the second air stream during a heating cycle. Other illustrative embodiments are contemplated, as further described below.